Abstract
The role of fatigue in injury development is an important consideration for clinicians.
In particular, the role of eccentric fatigue in stretch-shortening cycle (SSC) activities
may be linked to lower limb overuse conditions. The purpose of this study was to explore
the influence of ankle plantarflexor eccentric fatigue on SSC effectiveness during
a hopping task in healthy volunteers. 11 healthy volunteers (23.2±6.7 years) performed
a sub-maximal hopping task on a custom-built sledge system. 3D motion capture and
surface EMG were utilised to measure lower limb stiffness, temporal kinematic measures
and muscle timing measures at baseline and immediately following an eccentric fatigue
protocol. A linear mixed model was used to test whether measures differed between
conditions. Compared to baseline, eccentric fatigue induced increased stiffness during
the hopping task (+ 15.3%; P<0.001). Furthermore, ankle stretch amplitude decreased (– 9.1%; P<0.001), whilst all other ankle kinematic measures remained unchanged. These changes
were accompanied by a temporal shift in onset of activity in soleus and tibialis anterior
muscles (– 4.6 to – 8.5%; p<0.001). These findings indicate that eccentric fatigue alters SSC effectiveness in
healthy volunteers. These findings may be applied to inform pathogenetic models of
overuse injury development.
Key word
fatigue - stretch shortening cycle - eccentric contraction - stiffness
